Variable speed power transmission systems are commonly used in automotive and other applications in which accessories are driven from an engine by drive pulleys and a drive belt which is received on a driven pulley that is connected to the accessory. The conventional variable speed power transmission system allows the speed of the accessory being driven by the engine to be maintained more nearly constant notwithstanding that engine speed may be varied considerably during driving.
The variable speed power transmission systems commonly used in the past employ a pair of spaced, adjustable pulleys interconnected by V-belt arrangements in which the side edges of the V-belt, which generally form an included angle of 30.degree., cooperate with opposed side surfaces of pulleys that also form an included angle of 30.degree. between them and are relatively axially moveable toward or away from one another. Such movement of the pulley side surfaces toward or away from one another changes the effective diameter at which the V-belt rides on the pulley sides, thereby changing the speed relationship between the two pulleys, and the speed ratio between the driving engine and the driven accessory.
The foregoing systems, while satisfactory for purposes of driving accessories from an automotive engine, are limited in application due to the facts that they employ elastomeric V-belts as the load carrying members that extend between the driving pulley and the driven pulley, and that the power carrying capacity of conventional elastomeric V-belts is relatively low unless the belts are made prohibitively large in size. This limitation has become more pronounced and evident in recent years with the tendency for automative engines to be made smaller and to operate at higher load ratings, and has become particularly apparent in connection with the use of small engines which create maximum torque at and are operated at relatively high engine speeds. Rather than speeding up and slowing down the engines to effect speed changes of the vehicles, in these engines variable speed power transmissions can be employed to effect the necessary speed changes of the vehicle. These drive systems, termed constant velocity transmission drive systems, place large strains on conventional variable speed power transmission systems and lead to early failure of V-belts employed in such conventional variable speed power transmission systems when they are used in constant velocity transmission drive systems.
It is, therefore, a primary object of the present invention to provide an improved variable speed power transmission system which overcomes the deficiencies of prior forms of variable speed power transmission systems.
Another object of the present invention is to provide an improved power transmission pulley for use in an improved variable speed power transmission system.
A further object of the invention is to provide an improved power transmission pulley for use in an improved power transmission system and in which system a flat metallic belt may be substituted in place of the conventional V-belt as the driving belt of the variable power transmission system.
Additional objects and advantages of this invention will become apparent as the following description proceeds.